Δελτίο της Ελληνικής Γεωλογικής Εταιρίας τοµ. ΧΧΧΧ,
2007
Πρακτικά 11 ο υ Διεθνούς Συνεδρίου, Αθήνα, Μάιος 2007
Bulletin of the Geological Society of Greece vol. XXXX, 2007
Proceedings of the 11* International Congress, Athens, May,
2007
PETRIFIED WOOD OCCURRENCES IN WESTERN THRACE
AND LIMNOS ISLAND: MINERALOGY, GEOCHEMISTRY
AND DEPOSITIONAL ENVIRONMENT
1
2
2
3
Voudouris P. , Velitzelos D. , Velitzelos E. , and Thewald U.
1
National and Kapodistrian University of Athens, Faculty of Geology and Geoenvironment,
Department of Mineralogy - Petrology, voudouris @geo I. uoa.gr
2
National and Kapodistrian University of Athens, Faculty of Geology and Geoenvironment,
Department of Hist. Geology - Paleontology,velitzel@geol.uoa.gr
University of Ulm/Germany, Department of Chemistry, Section of "Röntgen und
Elektronenbeugung ", Ulf. Thewalt@chemie. uni-ulm. de
Abstract
The present study describes the geology and mineralogy of the main petrified wood
occurrences in Evros-Rhodopi and Limnos and integrates them in a volcanichydro thermal framework taking into consideration the nature of hydrothermal solutions during the silicification process. In the Lykofi-Fylakto-Lefkymi area, quartz
and opal-CT are the main silica polymorph within the wood. The hostrocL· exhibit a
zeolitic alteration suggesting reduced and slightly alkaline fluids for the silicification of wood. At Kassiteres/Sappes area the presence ofsilicified wood within kaolinite±alunite altered tuffbreccias indicates that slight acidic fluids were involved in
the silicification processes. In Limnos Island the fossiliferous Portianou, VarosRoussopouli and Moudros-Roussopouli areas occur in the periphery of an eroded
volcanic edifice exposed at Fakos peninsula. The silicified wood occurs: (a) within
weakly altered pyroclastics and (b) associated to several horizons of sinters interbedded within the pyroclastics. Transformation of amorphous silica to opal-CT and
then to quartz is postulated based on XRD and SEM studies. The studied areas represent unique natural monuments, comparable to the petrified forest of Lesvos island.
Key words: silicified wood, Evros, Limnos, mineralogy, depositional environment.
Περίληψη
Η παρούσα µελέτη περιγράφει την γεωλογία και ορυκτολογία των κυριώτερων εµφα
νίσεων απολιθωµένων δέντρων στους νοµούς Έβρου-Ροδόπης και τη νήσο Αήµνο,
και τις εντάσσει σε ένα ηφαιστειακό-υδροθερµικό πλαίσιο λαµβάνοντας επιπλέον υ
πόψη την φύση των υδροθερµικών διαλυµάτων που οδήγησαν στην απολίθωση. Στη
περιοχή Αυκόφης-Φυλακτού-Αευκίµης, χαλαζίας και οπάλιος-CT είναι τα κύρια πο
λύµορφα του πυριτίου που εντοπίστηκαν στα απολιθωµένα δέντρα. Τα πετρώµατα ξε
νιστές παρουσιάζουν µια ζεολιθική εξαλλοίωση, υποδεικνύοντας ότι υπεύθυνα για την
πυριτίωση των δέντρων ήταν αναγωγικά έως αλκαλικά διαλύµατα. Στις Κασσιτερές/Σαππών η παρουσία πυριτιωµένων κορµών εντός τοφφικών λατυποπαγών εξαλλοιωµένων σε καολινίτη±αλουνίτη, αποτελεί ένδειξη ότι στις διαδικασίες πυριτίωσης
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των δέντρων συµµετείχαν ελαφρά όξινα διαλύµατα. Στη νήσο Λήµνο, οι απολιθωµατοφόρες περιοχές Πορτιανού, Βάρος-Ρουσσοπουλίου και Μούδρου-Ρουσσοπουλίου
απαντούν στη περιφέρεια ενός διαβρωµένου ηφαιστειακού κέντρου που αναπτύσσεται
στην χερσόνησο του Φακού. Στη Λήµνο τα πυριτιωµένα δέντρα απαντούν: (α) εντός
ελαφρά εξαλλοιωµένων πυροκλαστικών και (β) σε σχέση µε πολυάριθµους ορίζοντες
πυριτικού sinter που παρεµβάλλονται µεταξύ των πυροκλαστικών. Μετατροπή άµορ
φου πυριτίου σε οπάλιο-CT και στη συνέχεια σε χαλαζία προκύπτει από µελέτες XRD
και SEM. Οι περιοχές που µελετήθηκαν αποτελούν µοναδικά φυσικά µνηµεία, συγκρί
σιµα µε το απολιθωµένο δάσος της νήσου Λέσβου.
Λέξεις κλειδιά: πυριτιωµένοι κορµοί, Έβρος, Λήµνος, ορυκτολογία, περιβάλλον από
θεσης.
1. Introduction
The northeastern Greece is a very promising district for the development of petrified forests, due
to its favourable geological setting and the extensive development of orogenic Tertiary volcanoplutonic arcs. This area is characterized by widespread occurrences of petrified forests, mainly in
the volcanic environments of northeastern Aegean (Evros, Limnos island, Lesvos island,
Velitzelos and Zouros 1997).
This study was focused on several localities from the two broad areas, Evros and Limnos: In Evros
there are several known occurrences east of Alexandroupolis, the Tychero, the Fylakto and also
near the Lefkimi areas among them (Fig. la). Other newly discovered occurrences are those of
Sapes and Perama areas (west of Alexandroupolis) and Aetochori/Pefka (east of Alexandroupolis)
indicating the widespread development of petrified forests in the whole region. In Limnos island
the main prospective area are the Moudros, Roussopouli, Romanou, Varos and Portianou areas
(Fig. lb).
In order to better understand the processes which resulted in the silicification of wood, this study
examines the characteristics of the magmatic-hydrothermal and geothermal systems that were
developed during the past in the studied areas. The evolution of these systems was the main factor
controlling the circulation of silica-enriched fluids responsible for the silicification of wood. The
present study describes the geology and mineralogy of some important petrified wood
occcurrences in northeastern Greece and integrates them in a volcanic-hydrothermal framework
taking into consideration the nature and chemistry of hydrothermal solutions during the
silicification process.
2. Materials and Methods
Laboratory research included optical microscopy, XRD analysis with a SIEMENS type D-500
instrument, SEM analysis using a DSM 962 Zeiss Digital Scanning Microscope, at 5kV, 0.74 nA
both performed in the Section of "Röntgen und Elektronenbeugung", Department of Chemistry,
University of Ulm/Germany. Selected samples were analyzed for major and trace elements using
XRF method with a Phillips PW 1220 instrument in the Institute of Mineralogy and Petrology,
University of Hamburg.
3. The geodynamic evolution and volcanic activity in northeastern
Greece
The geodynamic evolution in north-eastern Greece includes an early oceanic-continental
subduction/collision and post-Alpine extension resulting in the formation of back-arc basins in
Rhodope and Limnos island (Krohe and Mposkos 2001). Post-collisional extensional collapse of
the orogen resulted in the formation of several supra-detachment basins from the Lutetian (48 - 43
Ma) through the Oligocene up to the Pliocene. Slab break-off and/or slab delamination were principal
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mechanisms for the generation of extensive post-collisional magmatism in the area during the
Oligocene to Miocene times, which greatly influenced the development of magmatic-hydrothermal
systems (de Boorder et al. 1998, Pe-Piper et al. 1998, Melfos et al. 2002). The resulting plutonicsubvolcanic (monzonites, monzodiorites, granodiorites, microgranite porphyries) and volcanic
rocks (banakites, trachytes, andésites, dacites, rhyolites) in Evros region show calc-alkaline, highK calc-alkaline, to shoshonitic affinity (Innocenti et al. 1984, Christofides et al. 1998). New K/Ar
ages of volcanic rocks in this area range from 33.5 to 19.6 Ma, establishing an Oligocene and a
Lower Miocene period of magmatic activity (Pecskay et al. 2003). An enriched mantle source
region for the basic to intermediate magmas and a partial melting of crystal material for the acid
magmas has been documented. The magmatic rocks in the island of Limnos are of Lower Miocene
age (21-18 Ma) and display an orogenic character and calc-alkaline to shoshonitic affinity (Fytikas
et al. 1979, 1984, Innocenti et al. 1994). The geochemical character of the Limnos magmatic rocks
indicates fractional crystallization processes in the boundary between continental crust-mantle
related to an enrichment of the melts in K 2 0 and LILE elements.
4. Description of the petrified wood occurrences in Greece
4.1. Evros region
4.1.1. Regional geology
In Evros region the Cenozoic magmatic activity is closely related to the development of basincontrolled volcano-sedimentary formations which cover discordantly the basement rocks of the
RJiodope massif and Circum Rhodope Belt (Papadopoulos 1982). Initial sedimentation started at
Lutetian with the deposition of a basal-clastic formation, composed of conglomerates and
sandstones overlain by a Priabonian clay-marl formation including marls alternated with
sandstones and conglomerates and intercalations of lignitic horizons at the upper levels. The main
phase of the Tertiary magmatism took place during the Oligocene (Innocenti et al. 1984,
Kyriakopoulos 1987, Del Moro et al. 1988) and is represented by submarine/terrestrial volcanics
and subvolcanic rocks, associated with volcano-sedimentary series composed of marls, sandstones,
clays and intercalations of lavas, tuffs and pyroclastics.
4.1.2. Fylakto-Lykofi-Lefkimi-Dadia area
The geology of the area (Skarpelis et al. 1987) includes: a) a lower series of marine Priabonian
sediments, associated with andesitic lavas, b) pyroclastics and lavas of dacitic to rhyolitic
composition with intercalated sediments of Lower-Upper Oligocene age. The volcanics include
pyroclastic flows, air fall deposits, as well as lava flows and domes, c) Upper Oligocene shallow
marine sediments dominated by sandstones, marls and conglomerates (the Provatonas series),
discordantly covering the acid volcanics. The area is also dominated by ignimbrites of several
meters thickness.
The Lykofi - Fylakto - Lefkymi area is characterized by numerous occurences of silicified plant
fossils, hosted within the Oligocene volcano-sedimentary formations. According to Kopp (1965),
Velitzelos et al. (2002, 2006), the plant fossils are mainly related to the Rupelian-Chattian lignitebearing volcano-sedimentary strata of Provatonas series (SE of Fylakto village).
In the present study three fossiliferous localities were mainly investigated: the Vrysi-Pardalos
between Lyra and Lagyna (Fig. 2a), the Avgo-Pefkonas, about 500 m west of Fylakto (Fig. 2b)
and 3 km north of Lefkimi. In all these localities the petrified wood occurs within the volcanosedimentary formation of Provatonas series (Fig. 2c) covering discordantly the volcanics. A
shallow marine environment is indicated by the presence of coral reefs and also established by the
observation of abundant mollusks within the silt layers. In the locality of Vrysi-Pardalos (Fig. 2a)
silt strata with abundant leaves are overlain by sandstones and microconglomerates hosting trunks
of silicified wood. In the locality of Avgo-Pefkonas near Fylakto village a very similar stratigraphy
includes silt layers at the base, overlain by alternations of fine- to very coarse-grained volcano-
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sedimentary beds. Several trunks of silicified wood (up to 17 m long) occur within the volcanic
agglomerate formation, which is composed of subrounded silicified boulders of acid volcanic
rocks within a tuffitic matrix (Fig. 2c).
Figure 1 - (a) Geological sketch map showing the geology of the western Thrace (modified
after Melfos et al. 2002) and location of the petrified-wood occurrences (1, 2); (b) General
ized geologic map of Limnos island (modified after Innocenti et al. 1994) and the Moudros
(1), Varos-Roussopouli (2), Portianou (3) petrified-wood occurrences
Figure 2 - (a) Location Vrysi-Pardalos: A sedimentary succession from fine-grained strati
fied silt (bottom) to sandstones and volcanic microconglomerates rich in silicified wood (up
per parts); (b) Avgo-Pefkonas locality: Silicified trunk within volcanic agglomerate; (c) Rhyolitic lava overlain by volcano-sedimentary formation of Provatonas series; (d) Locality 3 km
west of Lykofi. Spherolites of initial amorphous silica (opal-Α) recrystallized to lepispheres
of opal-CT, SEM micrograph; (e) Clinoptilolite (clin) crystals filling vugs within silicified
coral-reef limestone, SEM micrograph, locality 3 km south of Lykofi; (f) Clinoptilolite (clin),
chalcedony (ch), opal (op) and pyrite (py) overgrown by calcite (cal). Wall-rock alteration of
dacitic lavas related to amethystine/chalcedonic veining. Kornofolia locality (SEM-BSE im
age)
In the Lefkimi locality, andesitic hyaloclastites (suggesting a submarine environment of formation)
are overlain by coral-bearing reefs and then by fine-grained volcano-sedimentary layers including
silicified wood. Volcanic agglomerate strata in the Hills around Lefkimi (similar to those
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described above) are very rich in silicified wood and also contain boulders of quartz-chalcedony
veins and of alunitic altered rhyolitic rocks.
It should be mentioned that the broad area is also characterized by abundant silicifications
indicating intense hydrothermal activity in a shallow submarine to subaerial environment during
the Upper Oligocene. The volcanic and volcano-sedimentary rocks (either of acid or intermediate
composition) are overlain by opalized coral-bearing limestone reefs outcropping in several
localities (e.g. south Lykofi). Both the opalized limestone and the underlying volcanic rock are
crosscut by chalcedony-quartz veins. In open spaces well-formed quartz and calcite crystals are
observed. The silicified zones in the broad area are accompanied by pyrite and marcasite.
The XRD analysis indicated that silicification of the studied wood material occurs mainly in the
form of quartz. Some opal-CT accompanying quartz was detected in the Avgo-Pefkonas locality.
A transformation from amorphous silica (opal-A) to lepispheres of opal-CT and finally to quartz is
suggested by SEM analysis (Fig. 2d). The hostrock exhibits a zeolitic alteration (including
clinoptilolite, mordenite, adularia, calcite, albite, opal-CT) (Figs 3 a, b), which seems to be
widespread in the broad area (see also Skarpelis et al. 1987). Quartz-chalcedony veins within
silicified coral reefs as well as within dacitic lavas from the broad area, also exhibit a zeolitic
signature (Figs 2e, f). Representative chemical analyses of zeolitic altered hostrocks and one
analysis of silicified wood from Fylakto area are presented in Table 1. Besides Si0 2 and H 2 0
(probably in the form of structural water in opal) the analysis of the wood material indicates
depletion in major and trace elements (sample Fyl7b, Table 1).
4.1.3. Kassiteres/Sapes area
The Kassiteres represents an intensively hydrothermally altered area, located near Sapes about
20 km NW of Alexandroupolis. It consists mainly of volcanic and intrusive rocks of intermediate
to acid composition. A thick volcanic sequence consisting of lava domes, flows and pyroclastics
dominates the western and northern part of the Kassiteres area. The close spatial relationship of
lava flows, domes, and pyroclastics with intrusive bodies of similar geochemical and
petrographical characteristics suggest that the Kassiteres area has been a volcanic centre, probably
a single or a composite stratovolcano.
The majority of magmatic rocks in the Kassiteres-Sapes area are intensively altered as a result of
repeated hydrothermal activity in the area. Alterations typical of high-sulfidation systems (White
and Hedenquist 1995) are characterized by an inner silicic zone (vuggy silica), surrounded
progressively by advanced argillic (quartz-alunite-kaolinite) and sericitic (quartz-sericite)
alteration (Fig. 4a). Intermediate sulfidation quartz and calcite veins with related K-feldspar
(adularia), sericitic and intermediate argillic alteration are developed below the advanced argillic
and silicic zones. Intermediate sulfidation quartz veins crosscut the silicic bodies. The veins
consist of amethystine/chalcedonic quartz with minor adularia, calcite and barite gangues (Figs 4b,
c). These veins are similar to those described from the Lykofi and Lefkimi areas.
Fossilized wood trunks were found on the south of Kassiteres within altered tuffitic material (Fig.
4d). The trunks are hosted in advanced argillically altered (kaolinite alteration) tuff-breccias
developed laterally of the silicic and alunitic alteration zone (Figs 4a, e, f). Quartz/chalcedony
veins including adularia and calcite crosscut the silicified trunks as well the silicified zones,
postdating their formation. Similarly to the results obtained from the Fylakto-Lefkimi area, the
silicification in the Kassiteres wood consists almost entirely of quartz. Chemical analyses indicate
total Si0 2 contents of 96.2-97.01 wt% whereas small amounts of A1203 and H 2 0 are attributed to
the presence of kaolinite (samples KassAl-A2, Table 1). Fe 2 0 3 up to 0.70 wt% is attributed to the
presence of iron oxides.
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Figure 3 - XRD diagrams indicating various mineral associations within volcanosedimentary rocks hosting sii ici tied wood, a) Avgo-Pefkonas: Quartz-c I inopti lolite alteration
of fine-grained volcano-sedimentary layer hosting woods; b) Avgo-Pefkonas: zeolitic alteration (mordenite+adularia) of volcanic fragment from the volcanic agglomerate hosting
woods; c) Kassiteres: Advanced argillic (quartz-natroalunite) alteration of tuff-breccia adjacent to the silicified wood; d) Kassiteres: quartz-kaolinite alteration of silicified wood hostrock; e, f) natroalunite in hydrothermaly brecciated silicic and advanced argillic alteration
zones from Moudros and Roussopouli areas
Figure 4 - (a) Silicic alteration (vuggy silica) surrounded and underlying by advanced argillic
(quartz-alunite, quartz-kaolinite) and sericitic (quartz-sericite-kaolinite) alteration). Location of silicified wood at Kassiteres area; (b) handspecimen showing co I loforni banding between amethystine and chalcedonic silica and quartz-adularia rich wallrock alteration
(10 cm long); (e) idiomorphic adularla crystals (ad) from the quartz-adularia alteration zone
of a dacitic andésite (+ niçois); (d) silicified wood within kaolinite altered tuff-breccia; (e)
laminated alunite crystals of replacement origin and quartz, west of Kassiteres (+ niçois); (f)
Platy alunite from the wallrock alteration of tuff-breccia hosting silicified wood
243
4.2. Limnos island
4.2.1. Regional geology
The geology of Limnos island is characterized by a sedimentary basement including molassic
deposits of Middle Eocene - Lower Miocene age, covered by volcanic products (lava domes, flows
and pyroclastics) of Lower Miocene age and by an Upper Quaternary sedimentary formation
(Davis 1960, Roussos 1993, Innocenti et al. 1994). A subvolcanic body of quartz monzonitic
composition intrudes the volcanics and sediments in the southern part of Fakos peninsula (Fig. lb).
Intense hydrothermal alteration and quartz veining in Fakos area (Voudouris and Skarpelis 1998)
are very similar to those described from Kassiteres in Evros region.
Most of the island is covered by volcanic rocks, subdivided (according to Innocenti et al. 1994)
into three major units: Katalako, Romanou and Myrina Units. The Romanou Unit is the main host
of the petrified woods in Limnos island. It consists of up to 160 m thick pyroclastic flow deposits,
which extent over broad areas mainly around the Moudros gulf (Fig. lb). This unit (intercalated
between the Katalako and Myrina units) is dominated at the base by white-colored pyroclastic
flows, rich in lithic components and pumiceous fragments, followed by intercalations of
ignimbrites, volcanic breccias and pyroclastis flows. The pyroclastic rocks of the Romanou Unit
are classified as K-rich dacites to latites and are radiometrically dated as 19.8 Ma old (Innocenti et
al. 1994).
4.2.2. Moudros-Roussopoufi-Varos-Portianou
Silicified wood-bearing pyroclastic beds are abundant on the eastern part of Limnos island (Figs
lb, 5). During this study three broad areas were examined, namely those of south Portianou, the
Varos-Roussopouli and Moudros-Roussopouli. The stratigraphy in these areas consists of tuffitic
layers at the base, overlain by volcaniclastic material (Figs 5a, b, d). In places lava domes and
flows penetrate the pyroclastics along the same orientation (NE-SW) as the fault zones in the area.
The broad Moudros-Roussopouli area is characterized by abundant manifestations of hydrothermal
activity, similar to those of Evros region. The following hydrothermal alteration zones were
distinguished: silicic, advanced argillic and argillic (smectite-kaolinite). The silicic alteration
zones (Fig. 5f) are wedge shaped and related to the fault systems developed on the area trending
N70E and N40W. It grades outwards to advanced argillic (alunitic), argillic (smectite-kaolinite)
alteration and then to fresh rock. The silicification is microcrystalline, massive with colours
varying between white, grey and black, the later due to the presence of disseminated pyrite and
marcasite. Alunite and anatase are minor constituents of the silicic alteration zone. The silicic
zones are crosscut by several hydrothermal breccia bodies, consisting of angular silicified
fragments surrounded by an iron oxide-rich matrix (Fig. 5i). In the silicic alteration zone no
fossilized wood have been observed. The alunite zone (sample M2, Table 1) is composed of silica
polymorphs, natroalunite, natrojarosite, and kaolinite (Figs 3e, f). Acicular alunite crystals (Fig. 5j)
occur together with quartz, kaolinite and pyrite as replacements of plagioclase, amphiboles, biotite
and pyroxene phenocrysts. Hydrothermal breccias also occur within the alunite zone. The
assemblage kaolinite-smectite-pyrte is well developed both laterally, as well as beneath the alunitic
zone.
Silicified wood occur in two distinct environments:
A) In slighly altered (argillic alteration) pyroclastics, and typical examples are found in Varos and
Portianou. Near Varos village several meters long trunks occur. The Portianou (and also Moudros)
localities include in situ silicified wood hosted within the pyroclastics (Fig. 5c).
B) In several layers of opaline, "silica sinter"-similar, silicification extending from Moudros to
Roussopouli. The fossiliferous zones [already described by Papp (1953)] are intercalated between
the pyroclastic beds and are up to 3 m thick each. At least six silica sinter horizons have been
recognized (Fig. 5d). According to Papp (1953) these horizons represent thin bedded lacustrine-
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ible 1 - Representative XRF analyses of silicified wood and wall-rocks from Evros and Limnos areas
Fyl7a
70.20
11.84
0.92
0.05
0.14
1.78
1.65
4.17
0.12
0.01
0.06
8.2
99.31
798
56
22
12
.32
9
20
52
262
161
12
4
16
18
22
85
Fyl7b
96.15
0.00
0.09
0.00
0.01
0.06
0.08
0.00
0.00
0.01
0.02
1.73
98.14
Fyl7c
76.41
12.36
0.74
0.01
0.35
0.39
0.49
2.44
0.21
0.01
0.02
5.59
99.13
KassAl
96.22
0.25
0.70
0.00
0.04
0.06
0.07
0.04
0.01
0.01
0.02
0
0
31
0
0
7
0
0
0
1
0
0
5
0
0
0
620
16
7
6
12
10
2
15
94
46
11
5
28
12
13
141
M-2
M7b
56.00
14.83
1.18
0.00
0.03
0.27
1.08
2.17
0.65
0.38
16.08
21.03
99.42
93.87
0.05
2.55
0.01
0.01
0.09
0.12
0.03
0.00
0.03
0.04
1.89
98.73
M14a
93.20
0.00
1.77
0.00
0.03
0.10
0.08
0.00
0.00
0.00
0.02
2.26
97.48
M14b
96.30
0.00
0.04
0.00
0.01
0.05
0.07
0.00
0.00
0.01
0.02
1.05
97.55
668
41
7
14
28
0
9
128
14
2288
1964
1637
10
14
139
9
0
89
19
5
119
6
0
466
197
11
57
3
0
8
0
0
1
20
0
3
28
0
26
0
47
1
111
1
16
5
0
0
0
5
0
3
8
0
31
0
14
0
46
1
7
6
0
0
1
4
1
1
1
0
0
0
98.83
KassA2
97.01
0.03
0.16
0.00
0.01
0.07
0.06
0.00
0.00
0.03
0.01
0.78
98.17
KassA3
70.21
18.69
0.18
0.00
0.01
0.15
0.10
0.07
0.53
0.32
0.07
7.67
98.33
47
0
40
2
0
9
1
0
0
7
0
0
6
1
0
2
10
0
36
2
4
6
0
0
0
4
0
0
6
0
0
0
1.4
164
36
15
100
2
48
80
24
trace elements in ppm; Fe203*= total iron as Fe 2 0;; Lyk5b: zeolitic altered acid volcanic rock, Fyl7a: zeolitic altered (mordenite+adularia)
: Avgo-Pefkonas, Fyl7b: silicified wood composed of opal-CT and quartz from Avgo-Pefkonas, Fyl7c: zeolitic altered matrix (quartz+adu
\vgo-Pefkonas. KassAl : silicified wood from Kassiteres, KassA2: silicified wood from Kassiteres, KassA3: advanced argillic altered (qu
iiteres. M2: advanced argillic altered rocks containing quartz+natrolalunite from Moudros, M7b: silicified wood, M 14a: Red opal horizon
ored silicified wood from the previous horizon, M21a: black colored silicification with plant material, M21c: silicified wood
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Figure 3 - Portianou locality, (a) A succession from volcano-sedimentary (sandstone like tuffite) to volcaniclastic material made up by angular to subangular andesite-dacite fragments,
(b) Close-up to the upper volcaniclastic formation as in Fig. 4a, (c) Silicified wood within the
basal tuffite. Moudros-Roussopoulis area: (d) Volcanic agglomerate formation at the base
(up to 20m thick) is overlain by pyroclastic flow units. Several fossiliferous opalized "sinter"
horizons (sint) are intercalated between relatively fresh volcanics (e) Close-up of the basal
volcanic agglomerate formation from previous figure, (f) View towards Roussopouli. Hypogene silicic and advanced argillic alteration zones, (g) Tilted opalized horizon rich in silici
fied wood overlies alunitized pyroclastics. (h) Opalized horizon including silicified wood
overlies pyroclastic material (i) Hydrothermal breccia composed of silicified and alunitized
rock fragments within a matrix rich in Fe-oxides. SEM-micrographs of various mineral
phases from Roussopouli-Moudros area, (j) Alunite crystals in vugs of advanced argillic al
tered rocks at Roussopouli (k) Lepispheres of opal-CT recrystallized after amorhous silica
(opal-Α) in advanced argillic altered hydrothermal breccia, near Moudros (1) Tridymite
(?) crystals on silicified wood from Moudros
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fluviatile intercalations between the pyroclastic formations and were deposited during erosional
periods that lasted between the volcanic activity phases. The pyroclastic hostrocks demonstrate
varying degrees of hydrothermal alteration. In some places the fossiliferous horizons overly an
alunitic alteration zone and hydrothermal breccias rich in natroalunite (Fig. 5g) whereas the wood
occurs as breccia fragments. Usually the opaline horizon is intercalated between fresh rocks.
Perfectly preserved leaves indicate quiescent conditions during the fossilization procedure. The
fossiliferous silicified horizons are crosscut by later chalcedony veins. Silicification in both the
"silica sinter", as well as within the wood material, varies from red and white, to black colour. The
white colour resulted of total depletion of iron oxides (see sample M 14b, Table 1). In general there
is a depletion of major and trace elements in silicified sinter and wood. Elevated Fe 2 0 3 content (up
to 2.6 wt%) is related to the presence of iron oxides and contributes to the red colour of the
silicification (Table 1). XRD-studies indicated mainly quartz as the stable silica phase within the
wood. Transformation of amorphous silica to opal-CT and then to quartz is postulated based on
XRD and SEM studies (Fig. 5k).
The field observations indicate that there is a close spatial and probably genetic relationship
between the silicic-alunitic alteration zones and the fossiliferous silica layers. In any case there is a
lateral transition and evolution of the above mentioned alteration zones laterally and upwards in
stratiform fossiliferous silicification.
5. Discussion-Conclusions
Recent studies confirmed that the silicification of wood begins as a process of open space filling
and not as a replacement of organic material by Si0 2 (Roessler 2001). It seems to be controlled by
diffusion of microscopic particles of Si(OH)4, (molecules) within the wood structure. Under this
aspect the deposition of Si0 2 could be resulted without destruction of the organic structure of the
wood. However in advanced stages of silicification a removal of organic material is also possible
(Roessler 2001).
This study demonstrates a close genetic relationship between the silicification processes leading to
petrified forests in Evros and Limnos, and the hydrothermal alterations which were developed
during the waning stages of volcanic activity. Alterations typical for magmatic-hydrothermal
systems cover extended areas in Evros region (Kassiteres-Sapes, Loutros-Pefka, and the StavrosGerakina locality northwest of Lefkimi) and Limnos island (Fakos peninsula and the MoudrosRoussopouli areas. These alterations have a mineralogy which indicates reaction of the volcanic
rocks with acid sulfate-chloride waters of magmatic-hydrothermal origin, with pH values even
smaller than 2 and at elevated temperatures (according to White and Hedenquist 1995). In addition
these fluids were generated after condensation of magmatic vapors rich in S0 2 and HCl in
groundwater present within the volcanic edifices. The late development of quartz-chalcedony rich
veins accompanying a K-feldspar (adularla) alteration of the wall-rocks (Kassiteres, LykofiLefkimi), is characteristic of deposition by more reduced and neutralized geothermal fluids. This
indicates an evolution from a reactive magmatic-hydrothermal system dominated by magmatic
gases, to a geothermal system that is dominated by meteoric and/or seawater, in common with
many other places in the world (Henley and Ellis 1983). Figure 6 shows the depositional
environment of silicified wood studied, within a volcanic-hydrothemal framework.
The silicified wood observed south of the Kassiteres area, occurs within argillically altered
(kaolinite alteration) tuffs and in close proximity to silicic and advanced argillic alteration zones.
Available data indicate that silicification of wood in Kassiteres took place in a two-stage
procedure: firstly by slightly acid fluids as they were migrating away from the advanced argillic
alteration zone, and secondly by more reduced and neutralized fluids as late quartz-chalcedony
veins crosscuting the wood. A similar process has been also described for the silicification of
wood in Chemnitz, Germany (Roessler 2001).
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Basement
Quartz ± afunite iithccap
Y
Volcanic rocks
Qtz-Monzodiorite
t
Rhyolite porphyry
K-Na-sificate alteration
Advanced argillic
alteration
Magmatic-hydrothermai fluids
1 km ~
~
~
Acidic magmatic gases
hydrothermal fluid
Meteoric water & Seawater
Silica sinter
1 km
Figure 4 - Hypothetical model demonstrating depositional environment of silicified wood
occurrences in Kassiteres (1), Lykofi-Fylakto-Lefkimi (2) and Limnos island (3)
In contrast to Kassiteres area, the fossilized occurrences of Fylakto, Lefkimi, etc., are lying some
km away from the supposed highly reactive magmatic-hydrothermai center near Stavros locality.
Responsible for the silicification of trees were reduced and near neutral pH fluids as demonstrated
by the alteration mineralogy of the broad area (zeolitic alteration). Reduced and near neutral pH
fluids were also depositing the abundant quartz-chalcedony veins crosscuting all the formations in
the broad Fylakto-Lykofi-Lefkimi area.
In Limnos island, the Fakos peninsula has been recognized as a Cenozoic magmatic-hydrothermai
center with characteristics comparable to those of Kassiteres area. The central parts of the volcanic
edifice are occupied by silicic and advanced argillic alteration zones of magmatic-hydrothermai
origin. The silicified wood occurs in the periphery of Fakos but in very close proximity to large
scale fault zones that facilitated the circulation of hydrothermal fluids. Although the petrified
trunks found within relatively fresh pyroclastics, could have been formed partly by devitrification
processes by near neutral pH fluids, a hydrothermal deposition of silica is established for the wood
present in the silicified horizons between Moudros and Roussopouli. The silicified horizons
probably correspond to swamp depressions, which were flooded by the upwelling hydrothermal
fluids. Field observations indicate a scenario of contemporaneous formation between the horizons
and the silicic and advanced argillic alteration zones in a hot spring environment. The horizons
probable represent lateral surface manifestations of the above alteration zones. Neutralization was
resulted as the fluids migrated away from the acidic outflow zones. Alternatively some of the
horizons could represent true silica sinter formations (like the Rhynie chert in Schottland, Rice et
al. 2002), deposited from near neutral fluids and not directly related to the silicic and advanced
argillic alteration zones. This scenario requires distinct periods of formation and is a matter of
further investigation. The Evros and the Moudros-Roussopouli areas represent unique natural
monuments in Greece, comparable to the Lesvos island petrified forest (Velitzelos et al. 2002) and
belong to the Greek mineralogical and geological heritage. Ongoing work aims to constrain the
details about the mechanisms resulting in the silicification of wood in Evros and Limnos regions.
6.
Acknowledgments
Mrs G. Doerfner is especially thanked for the XRD measurements in the University of Ulm.
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